Why Do Ships Break From The Middle?

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Credit: marine insight

The biggest shipping loss to date occurred in the form of MOL Comfort in 2013.The MOL Comfort was caught in bad weather 200 miles off the coast of Yemen. Around dawn, it cracked in the middle and broke in two parts.

 

Understanding the Hull Girder Design

When a beam is loaded, it will either bend or flex, which means one part will be under compression, and the other will be in tension. When a ship’s hull girder is designed, the designers analyse the structure as a beam.

The buoyancy on the ship varies periodically along the ship’s length. A vessel should be designed keeping in mind the uncertainty of the loads. A hull girder is always supported by an “elastic foundation,” a sea surface. There is more buoyancy at the midship region than at the fore and aft end.

Safeguarding the Hull Girder Integrity

The shear force on any transverse section of the hull girder is zero at the aft end, fore-end and midships.

Bending Stress Concentration: The bending moment is always maximum at the midship. Due to this effect, the bending stress always reaches a maximum at the midship region of any ship, irrespective of its loading condition.

The magnitudes may vary, but this nature is followed through any loading condition the ship encounters in its lifetime.

Accidents and Grounding Impact: A ship may experience structural failure and water ingress due to accidents, increasing the load on its structure. When the already high bending stress at midship exceeds safe limits, the ship may break.

Grounding incidents can result in midship cracks or split-offs due to unwanted load distributions along the hull. This causes hogging or sagging, modes of bending that can lead to hull girder failure. Poor ship design and material choices can also contribute to ship splitting when loaded with cargo, as seen in the case of MOL Comfort.

The Role of the Chief Officer: The bending stresses should always be kept in check. The chief officer, in charge of the ship’s stability, must ensure the stresses are within the permissible limit. For this, loading manuals are provided, which are a guide to loading the ship by the design standards.

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Source: Marine Insight